(1) Field of the Invention
The present invention pertains to a photoelectric sensor and a restriction in a conveyor path that are parts of a conveying system. The sensor senses objects having triangular cross sections that are conveyed past the sensor by the conveyor system and the conveyor path restriction positions the conveyed triangular shaped objects where they can be engaged by a hold back gate.
(2) Description of the Related Art
The conveyor sensor and conveyor path restriction of the invention may be employed in any part of a conveyor system that conveys objects having irregular shaped cross sections to sense objects conveyed by the conveyor system and position the objects in the conveyor path where they can be engaged by a hold back gate to hold back objects conveyed by the conveyor system, but in the preferred embodiment of the invention the sensor and restriction are employed on an infeed conveyor that supplies several rows of objects having triangular shaped cross sections to a row former of a conveyor system.
Row formers are typically used in conveying systems that convey objects, for example light-weight blow molded plastic containers, in one or more single file streams of the objects from one station of the conveying system to another, for example, from a blow molding station where the containers are formed to a downstream palletizing station where the containers are arranged on pallets. The row former receives the objects from the one or more single file streams of objects conveyed by an infeed conveyor, arranges predetermined numbers of the objects in rows, and positions the rows side-by-side on a row accumulating table forming two dimensional arrays of the objects. Each two dimensional array of the objects is then typically swept as a layer of objects onto a pallet, becoming one layer of objects among the stacked layers of objects loaded onto the pallet.
The typical infeed conveyor is comprised of one or more conveyor belts on which numbers of the objects are conveyed in single file lines to the row former. The typical row former receives the streams of objects conveyed by the infeed conveyor belts and arranges numbers of objects in rows and then positions sequentially arranged rows of the objects side-by-side on the accumulating table of the conveyor system, forming a two dimensional array of the objects that are later palletized.
The row former includes one or more pairs of spaced, parallel arms or pusher bars that define one or more row forming slots between the arms for each line of objects conveyed by the infeed conveyor. The arms are positioned above the infeed conveyor where the slots between the arms receive numbers of objects from the streams of objects conveyed by the infeed conveyor. With the desired numbers of objects filling the slots of the row former, the conveyed streams of objects are held back by closing hold back gates of the infeed conveyor and the row former, with the arranged rows of objects, moves in a direction perpendicular to the rows a short distance across the infeed conveyor and onto a surface of the accumulating table. The arms of the row former then stop and move upwardly from the accumulating table, leaving the numbers of objects in the first arranged rows of objects on the table surface.
The row former arms are then moved in the opposite direction back across the accumulating table surface to their positions in line with the infeed conveyor conveying the streams of objects to the row former. The arms are then moved downwardly aligning the slots between the pairs of arms again with the infeed conveyor conveying the streams of objects to the row former. The gates of the infeed conveyor are opened and the slots between the row former arms are again filled with predetermined numbers of objects, following which the gates of the infeed conveyor are closed. The movement of the row former arms described above is then repeated, leaving numbers of objects in the second arranged rows on the accumulating table surface. This movement of the row former is repeated in forming a two dimensional array of the objects on the accumulating table surface.
Prior art infeed conveyors and row formers have worked well in arranging numbers of objects in rows and then positioning the rows side-by-side in forming a two dimensional array of the objects where the objects being formed in the array are symmetric about their center vertical axes. Plastic blow molded bottles and other such containers that are symmetric about their center vertical axes are examples of such objects. In forming rows of desired numbers of symmetric objects, photoelectric sensors could be positioned adjacent the hold back gates of the infeed conveyor and before the openings of the slots between the pairs of row former arms, with the beams of the sensors directed perpendicularly across the infeed conveyor paths to count the number of objects conveyed from the infeed conveyor into each slot of the row former by each object breaking the beam.
However, difficulties were encountered in forming rows of objects when the shapes of the objects changed from the conventional shape, symmetrical about its center axis, to asymmetric shapes, for example a plastic, aluminum or cardboard container having a triangular cross section. Containers with necks such as bottles enable a photosensor beam to be passed between the necks of the bottles conveyed in front of the photosensor to generate signals used in counting the bottles conveyed past the sensor. Straight walled containers such as jars or aluminum cans provide a predictable curved surface at their sides that enable the use of proximity sensors in sensing the containers conveyed in front of the proximity sensors and providing signals for counting the containers conveyed past the sensors. However, for objects like containers having straight walls and irregular shaped cross sections such as triangular cross sections, a beam of a photosensor cannot pass between adjacent containers in a conveyed stream and a proximity sensor would provide different proximity signals depending on whether the sensor was sensing the smaller apex of a container or the larger side wall of a container passed by the sensor.
A side view of one example of a container 10 having a triangular cross section is shown in FIG. 1. The container 10 is basically comprised of a hollow triangular body 12 having an enlarged base 14 at its bottom and an enlarged rim 16 around a top opening of the container. Single file streams of these containers would be supplied by the infeed conveyor to the slots between the row former arms with the containers of each stream of containers positioned relative to each other as shown in FIG. 2. FIG. 2 is a schematic representation of the positions of the containers in four streams of containers supplied by the infeed conveyor to the four slots of a row former. As seen in FIG. 2, adjacent containers of each of the four rows of containers are rotated 180 degrees relative to each other to maximize the number of containers that can be arranged in each row of the row former. However, although the arrangements of the containers in each row shown in FIG. 2 maximize the number of containers occupying each row of the row former, problems arose in supplying desired numbers of the containers from the infeed conveyor into the slots of the row former.
The triangular cross section shape of the containers presented the problem of how to count the number of containers supplied by the infeed conveyor to each row of containers formed in a row former slot. Prior art container counters employed photoelectric sensors that emit beams across the infeed conveyor at their hold back gates generally perpendicular to the direction of travel of containers passing through the infeed conveyor gates and entering into the row former slots. The overlapping arrangement of the triangular containers shown in FIG. 2 would prevent a beam of a prior art sensor from passing between two adjacent containers. Referring to FIG. 3, with two sequential containers 10 in a stream of containers being conveyed in the direction indicated by the arrow D, it can be seen that the prior art arrangement of positioning a photoelectric sensor to emit a beam, represented by the line A—A, across the stream of objects to count the numbers of objects conveyed will not work for containers having triangular shaped cross sections. As illustrated in FIG. 3, the overlapping arrangement of adjacent triangular shaped containers will prevent a beam directed perpendicularly across the conveyor path from passing between adjacent conveyors. Thus, changes were required from the prior art means of counting containers to determine the numbers of containers having triangular shaped cross sections that were supplied through the infeed conveyor gates to each row of the row former slots.
In addition, in using the arrangements of the containers shown in FIG. 2 in each conveyed path of the infeed conveyor supplying desired numbers of objects to the rows of the row former, problems arose when the rows of containers were moved by the row former from the infeed conveyor to the accumulating table surface of the conveyor system.
When the rows of containers arranged as shown in FIG. 2 were moved to the accumulating table surface and pushed across the table surface by subsequent rows of containers formed by the row former, the point contact between the apexes of containers in one row with the side walls of containers in the adjacent row would cause the containers to move away from their relative positions shown in FIG. 2. This was primarily due to the single point contact of the apex 18 of a container in one row pushing against the middle of a side wall 20 of a container in an adjacent row and the single point contact between the middle of a side wall 20 of a container in one row pushing against an apex 18 of a container in the adjacent row. The single point contact of the apex 18 with the side wall 20 would cause the container pushed by the adjacent container to tend to rotate or move to one side or the other of the apex as the containers are pushed across the accumulating table surface.
To overcome the problem of movement of the triangular containers relative to each other as an array of the containers was pushed across the accumulating table surface by the row former, the inventor of the subject matter of the application created a novel arrangement of the triangular containers. In the novel arrangement of the containers, the containers are not arranged in an array of rows that extend straight across the two dimensional array with the side walls and apexes of adjacent containers in each row being positioned in a single vertical plane as shown in FIG. 2, but the containers of each row are arranged in a staggered arrangement shown in FIG. 4. The staggered arrangement of the containers shown in FIG. 4 provides a more stable two dimensional array of the containers than that of the array of FIG. 2. In the staggered array of FIG. 4, the side walls 20 of the containers in each row pushed by the apexes 18 of the containers in the adjacent row are also contacted at their opposite ends by the two containers on opposite sides of the container making apex contact. Also, the side wall 20 of each container in one row that pushes against an apex 18 of a container in an adjacent row also pushes against the two containers on opposite sides of the container with which it makes apex contact. Thus, the additional points of contact between the containers in adjacent rows prevents the containers being pushed from rotating to either side and provides a more stable two dimensional array of containers pushed across the accumulating table surface that maintains their relative positions as they are pushed across the accumulating table surface.
However, the array arrangement shown in FIG. 3 presents the problem of how to establish the staggered relationship of the containers 10 in each row of the row former that will enable the row former to push staggered rows of containers arranged as shown in FIG. 4 onto the accumulating table surface. In order to provide a smooth transition from the infeed conveyor to the row former, guide rails on opposite sides of each conveyed path of the infeed conveyor must align with the pusher arms or pusher blades of the row former. However, to provide sufficient room between the pairs of opposed row former arms to enable the rows of containers formed between the arms to assume the staggered configuration of each row of containers shown in FIG. 4, the spacing between the opposed arms of the row former must be larger than a width dimension of the containers measured between the apex and opposite side wall of a container. FIG. 5 shows a row former 22 having pairs of pusher arms 24 or pusher blades that define the row former slots 26 between opposed pairs of arms. Opposed arms 24 are spaced from each other to create the staggered rows of the containers 10 shown in FIG. 4. With this spacing between the arms 24 of the row former 22, the side walls 20 of adjacent containers formed in rows between each pair of arms engage against one of the opposite arms and the apex 18 of each container is spaced by a predetermined gap 28 from the other arm, thereby creating the staggered configuration of the containers in the rows shown in FIG. 4. However, by spreading out the opposed pairs of arms of the row former to allow a gap 28 adjacent the apexes of the containers formed in rows between the arms, it would also be necessary to spread out the guide rails of each conveyed path of the infeed conveyor so that the infeed conveyor guide rails would also align with the pusher arms of the row former.
Moving the guide rails of the infeed conveyor further apart so that they align with the pusher arms of the row former would result in the infeed conveyor hold back gates mounted on one of the guide rails of each infeed conveyor path being moved by the distance of the gap 28 further away from the opposite infeed conveyor guide rail. Widening the space between the infeed conveyor guide rails would also enable the containers conveyed by the infeed conveyor to move from side to side as they are conveyed between the guide rails. This presented the problem of the possibility of containers passing by the hold back gate of the infeed conveyor when the gate has been moved to its closed position. This potential problem could not be overcome by increasing the length of the infeed conveyor hold back gate because the length of the gate must be short enough to enable the gate to pass into the cleft 30 formed between adjacent containers to close the gate quickly once the desired numbers of containers delivered by the infeed conveyor to the row former had passed the infeed conveyor sensors.